1. Field of the Invention
This invention relates to an apparatus and method for evaluating the backface signature of flat panel ballistic resistant composites in correlation to the expected backface signature of shaped ballistic resistant composites in actual field use.
2. Description of the Related Art
In the field of body armor, there are an increasing number of suitable materials assembled or converted into ballistic resistant articles. These ballistic resistant articles include soft body armor for protection of the torso and extremities against certain threats, molded rigid plates which protect the torso against higher level threats, and molded rigid helmets which protect the head against a variety of threats. It is known that in addition to stopping bullets or projectiles, it is desirable for the armor to limit or minimize its own deflection back into the wearer during a ballistic event. This deflection is known in the industry as trauma, blunt-force trauma, backface deformation or backface signature (BFS). In the area of soft body armor, the article typically rests directly on or very close to the body of the user, and thus a reasonable approximation or prediction of BFS that may be expected during a ballistic event in field use may be measured by laying the article directly on a flat block of an deformable, oil-based clay, firing a projectile into the article, and then measuring the depth or volume of the resulting hole in the clay block. In the area of molded rigid armor, the same protocol may be used to obtain a reasonable approximation or prediction of BFS that may be expected during a ballistic event in field use for molded armor that rests directly on or very close to the body of the user.
However, such an approximation or prediction of BFS for rigid helmet armor is much more difficult because by rule the armor component of the helmet does not lie directly on the head of the user. Conventionally, helmets are designed with a variable off-set or stand-off distance that will vary due to the size and shape of the helmet interior relative to the size and shape of the head of the user. The minimum distance will generally be set or defined by a series of pads attached to the interior of the helmet, and an interior harness or retention system may increase this distance even more. Methods to measure the BFS of a prototype or finished helmet have been developed to approximate BFS of shaped helmets in a real end-use environment. One accepted technique begins with a metallic head form that has large sections removed. These sections are filled with clay and the clay is smoothed to a reasonable approximation of the contour of the human head. A prototype helmet is then placed on this head form and tested. Measurement of the depth and volume of the holes in the clay should give a reasonable approximation of the BFS that will be expected in field use when the helmet encounters a projectile.
As new materials are developed and evaluated, it is not always desirable, cost effective or prudent to fabricate a prototype helmet from each material intended for BFS testing. It is much simpler and thus preferred to conduct initial screening on molded flat panels, which are easier to produce, easier to work with during testing, and result in a hole or deformation that is easier to measure and evaluate. Unfortunately, data has shown that measurement of BFS using molded flat panels placed directly on clay does not correlate well with the actual in field helmet performance of materials. The present invention provides a solution to this problem in the art, providing an apparatus and method for testing molded flat panel composites for accurately determining the expected backface signature of ballistic resistant composites in actual field use, and avoiding the current need to produce helmet prototypes.